In many epithelial cells, the rate of sodium reabsorption is governed by the activity of the epithelial sodium channel (ENaC). ENaC activity is governed by a wide variety of physiologic conditions and hormonal influences. The goal of the following research project is to characterize the trafficking of ENaC in renal epithelial cells. Many studies have looked at the regulation of ENaC activity, but it has been found to be very complex and a more detailed understanding is lacking. Our laboratory and others have some data suggesting that there may be differential expression of ENaC subunits in assembly and trafficking. We are proposing a novel approach to study ENaC expression using polarized, hormonally responsive MDCK cells. We will use replication-defective recombinant adenoviruses to express individual ENaC subunits or combinations of subunits in MDCK cells; the advantages of this approach are that it allows us tremendous flexibility in expressing various combinations of channel subunits in controllable levels. We will be using this system to better study the delivery, turnover and recycling of subunits on the apical surface. The data that we will gather will provide an important comparison to previous studies done in oocytes. Together, these data will demonstrate whether ENaC channel composition is fixed or fluid and address the questions of where and how ENaC channel assembly is regulated.